1. Field of the Invention
This invention relates to a homogeneous process for the homologation of methanol to at least one of acetaldehyde, ethanol or methyl acetate. More particularly, methanol is treated with CO or CO/H.sub.2 mixtures in the presence of catalytic amounts of an iron-cobalt cluster compound and an iodide promoter.
2. Description of the Prior Art
The homologation of methanol to ethanol was first described by Wender et al, Science 133, 206 (1951). The catalyst for the reaction was dicobalt octacarbonyl. The product selectivities and catalyst efficiencies, however, were relatively low. It was subsequently discovered that product yields could be improved by the addition of small amounts of iodide promoters (J. Berty et al, Chem. Tech. (Berlin), 8, 260 (1956)). The production of ethanol from methanol using ruthenium and/or osmium complexes in the presence of iodides as co-catalysts is described in Japanese Pat. No. 52-73804. The reaction of methanol with synthesis gas has been discussed by I. Wender in Catal. Rev-Sci. Eng., 14, 97 (1976).
The carbonylation of methanol to acetic acid and methyl acetate using a cobalt acetate-iron acetate catalyst is described in Russian Pat. No. 437745. U.S. Pat. No. 3,332,749 (G. Natta and P. Chini) discloses iron-cobalt metallocarbonyl compounds of the formula R[FeCo.sub.3 (CO).sub.12 ] where R is a cation or H. U.S. Pat. No. 3,856,856 teaches the production of carboxylic acids and esters thereof by contacting aliphatic alcohols and carbon monoxide at elevated temperature and pressure in the presence of a platinum promoted cobalt/iodide catalyst system. Canadian Pat. No. 709,857 relates to an improved process for the preparation of acetic acid or mixtures thereof with methyl acetate by carbonylating methanol, methyl acetate or dimethyl ether using an iron group metal carbonyl plus halogen as catalyst.
It would be desirable to convert methanol to ethanol, acetaldehyde or methyl acetate with a high degree of selectivity, thus avoiding the substantial amounts of broad product mixture characteristic of known catalysts especially heterogeneous catalysts. Moreover, the catalyst should function with a relatively high degree of catalyst efficiency with respect to methanol conversion.